GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2008 🢒 Vibe - FWD 🢒 Safety and Security 🢒 Supplemental Inflatable Restraints 🢒 DTC B2798

Circuit Description

The ignition key has a transponder chip that allows the key code to be transmitted to the transponder key ECU assembly to allow engine start. If communication between the key and the transponder key ECU assembly is not possible, DTC B2798 is set.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC B2798 Communication Malfunction No. 2

Conditions for Running the DTC

This DTC shall run when key is inserted into key cylinder.

Conditions for Setting the DTC

DTC B2798 - Communication error

Action Taken When the DTC Sets

The engine will not start.

Conditions for Clearing the DTC

The DTC will clear when conditions for setting the DTC have been repaired.

Step

Action

Value(s)

Yes

No

Schematic Reference: Immobilizer Schematics

Connector End View Reference: Immobilizer Connector End Views

1

Did you perform the Diagnostic System Check - Vehicle?

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Go to Step 2

Go to Diagnostic System Check - Vehicle

2
  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With the scan tool, observe the Immobilizer State parameter in the Immobilizer data list.

Does the Immobilizer State parameter display Locked?

--

Go to Step 9

Go to Step 3

3

Check to see if other key that is good will start the engine.

Was engine started with other key?

--

Go to Step 4

Go to Step 5

4

Attempt to re-register the key. Refer to Immobilizer System Component Programming .

Does the re-registered key start the vehicle?

--

Go to Step 10

Go to Step 7

5
  1. Turn OFF ignition.
  2. Disconnect the transponder key amplifier and the transponder key ECU assembly connectors.
  3. Measure the resistance between the transponder key amplifier and transponder key ECU assembly as follows:
    4. • ECU terminal 4 to amplifier terminal 5
    • ECU terminal 5 to amplifier terminal 7
    • ECU terminal 14 to amplifier terminal 1
    • ECU terminal 15 to amplifier terminal 4
  4. Measure the resistance between the transponder key ECU assembly terminals and ground as follows:
    5. • ECU terminal 4 to ground
    • ECU terminal 5 to ground
    • ECU terminal 14 to ground
    • ECU terminal 15 to ground

Is the resistance measured less than or greater than the specified values?

ECU to amplifier = 1 Ohm or less

ECU to ground = 10 Kohms or greater

Go to Step 8

Go to Step 6

6

Test the applicable circuit for an open/high resistance or short to ground. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 10

Go to Step 9

7

Important: New key will have to be registered.

Replace the key.

Did you complete the replacement?

--

Go to Step 10

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8

Replace the transponder key amplifier.

Did you complete the replacement?

--

Go to Step 10

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9

Replace the transponder key ECU assembly.

Did you complete the replacement?

--

Go to Step 10

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10
  1. Use the scan tool in order to clear the DTC.
  2. Operate the vehicle within the Conditions for Running the DTC, as specified in the supporting text.

Does the DTC reset?

--

Go to Step 2

System OK